Typical four stroke outboard motors have several components that compete for common design space beneath the engine. For example, the exhaust conduit for conveying hot exhaust gas from the engine, the cooling water jacket for cooling exhaust gas in the exhaust conduit, the upper engine mounts, the oil pump, the engine oil sump, and engine oil drain back area all require space just below the internal combustion engine. These components are typically incorporated into a molded engine adapter plate that connects the engine to a housing for the driveshaft. The present inventor has recognized that this competition for design space at the location of the engine adapter plate usually compromises the design of the outboard motor, with added cost, reduced function, reduced performance, or a combination of these factors.
In order to achieve small-sized outboard configurations, typical outboard motors incorporate an engine cylinder block that is rotated so that the engine cylinders are not aligned with a vertical fore-aft central plane extending through the crankshaft. In these configurations, the exhaust conduit for conveying hot exhaust gas from the engine is located apart from the central plane. In fact, even in configurations where the engine cylinder block is not rotated, the exhaust conduit is located apart from the central plane to a certain extent. This off-center exhaust conduit must be routed back into alignment with the central plane at the bottom of the driveshaft housing in order to align with an exit port in the lower unit gear case.
The present inventor has recognized that routing the exhaust conduit back into alignment with the noted central plane undesirably places design constraints on the engine adapter plate, requires a great deal of space, often requires cover plates with screws and gaskets, and can often require sharp, flow-restricting corners in the exhaust conduit. These design constraints also often undesirably require location of the engine mounts at least partially in the exhaust conduit. As the engine adapter plate is utilized to bring the exhaust conduit into alignment with the central plane, the exhaust conduit is often in the way of the engine mounts. Further, placing the exhaust conduit though the center of the oil sump often wastes space and causes the sump to be longer and more expensive to form—in order to obtain a requisite oil volume. The present inventor has found that this is also true in cases where the sump has a “U” shape around the exhaust conduit. Further, U-shaped sumps often undesirably require increased fasteners to maintain a longer sealing flange that accompanies the U-shaped sump.
The present disclosure provides improved outboard motor configurations and exhaust system configurations. In one example, an outboard motor comprises an internal combustion engine, a driveshaft housing and a molded adapter plate connecting the internal combustion engine and the driveshaft housing. An elongated exhaust conduit conveys hot exhaust gas from the internal combustion engine. The exhaust conduit extends from a first end portion located proximate to the internal combustion engine to a second end portion located proximate to the driveshaft housing. The exhaust conduit and adapter plate are separate or segregated components.